1. Field of Invention
The present invention relates to a tandem master cylinder for hydraulic brake systems, the housing of which is securable to a booster housing of a preceding brake power booster. This tandem master cylinder has a primary piston prestressed by a return spring as well as a secondary piston which define, within a longitudinal bore, primary and secondary pressure chambers which in the release position are in connection with a supply tank through tank connections and hydraulic fluid ducts in the housing and being released, respectively, shut off by means of two valves which are actuatable by the primary piston.
2. Description of the Prior Art
A tandem master cylinder of this kind is known from German patent specification No. 23 35 530. A particular feature of this prior-art tandem master cylinder is that the valves disposed in the connection between the pressure chambers and the supply tank are actuated by a push rod which is guided within a bore extending parallel to the longitudinal bore of the tandem master cylinder and which is connected to the primary piston through a travel booster exclusively actuatable by the primary piston and has its fixed point at the housing such that in the event of actuation of the primary piston in the operating direction, the valves are closed in that the push rod is shifted by a distance which is greater than and proportional to the travel of the primary piston in respect of the housing.
In the state-of-the-art tandem master cylinder, the precision machining of the longitudinal bore and of the surfaces of the two pistons, on one hand, as well as of the bore accommodating the push rod, on the other hand, which is required for smooth operation of the tandem master cylinder and which involves heavy manufacturing cost must be regarded as disadvantageous.
The fact that the two pistons do not permit exact positioning relative to each other since the subdivision of their travel exclusively depends on the return springs by which they are prestressed is, furthermore, felt to be a disadvantage.
Another disadvantage is that the individual closing travels of the two valves which are determined by the tolerances are not adjustable, and that it is not possible to pre-assemble a plurality of components in order to optimize the assembly costs.